From eafb70d79042958235221a1428545253adc2220f Mon Sep 17 00:00:00 2001
From: Johan Walles <johan.walles@gmail.com>
Date: Sun, 19 Mar 2023 11:56:54 +0100
Subject: [PATCH] Configurable side scroll amount

Using the new --shift command line flag.

Fixes #130.
---
 m/pager.go | 33 ++++++++++++++++++---------------
 moar.1     |  3 +++
 moar.go    | 19 +++++++++++++++++++
 3 files changed, 40 insertions(+), 15 deletions(-)

diff --git a/m/pager.go b/m/pager.go
index 131d5334..7615b74d 100644
--- a/m/pager.go
+++ b/m/pager.go
@@ -74,6 +74,8 @@ type Pager struct {
 	ScrollLeftHint  twin.Cell
 	ScrollRightHint twin.Cell
 
+	SideScrollAmount int // Should be positive
+
 	// If true, pager will clear the screen on return. If false, pager will
 	// clear the last line, and show the cursor.
 	DeInit bool
@@ -142,7 +144,7 @@ func (pm _PagerMode) isViewing() bool {
 	return pm == _Viewing || pm == _NotFound
 }
 
-// NewPager creates a new Pager
+// NewPager creates a new Pager with default settings
 func NewPager(r *Reader) *Pager {
 	var name string
 	if r == nil || r.name == nil || len(*r.name) == 0 {
@@ -151,14 +153,15 @@ func NewPager(r *Reader) *Pager {
 		name = "Pager " + *r.name
 	}
 	return &Pager{
-		reader:          r,
-		quit:            false,
-		ShowLineNumbers: true,
-		ShowStatusBar:   true,
-		DeInit:          true,
-		ScrollLeftHint:  twin.NewCell('<', twin.StyleDefault.WithAttr(twin.AttrReverse)),
-		ScrollRightHint: twin.NewCell('>', twin.StyleDefault.WithAttr(twin.AttrReverse)),
-		scrollPosition:  newScrollPosition(name),
+		reader:           r,
+		quit:             false,
+		ShowLineNumbers:  true,
+		ShowStatusBar:    true,
+		DeInit:           true,
+		SideScrollAmount: 16,
+		ScrollLeftHint:   twin.NewCell('<', twin.StyleDefault.WithAttr(twin.AttrReverse)),
+		ScrollRightHint:  twin.NewCell('>', twin.StyleDefault.WithAttr(twin.AttrReverse)),
+		scrollPosition:   newScrollPosition(name),
 	}
 }
 
@@ -262,10 +265,10 @@ func (p *Pager) onKey(keyCode twin.KeyCode) {
 		p.handleScrolledDown()
 
 	case twin.KeyRight:
-		p.moveRight(16)
+		p.moveRight(p.SideScrollAmount)
 
 	case twin.KeyLeft:
-		p.moveRight(-16)
+		p.moveRight(-p.SideScrollAmount)
 
 	case twin.KeyAltRight:
 		p.moveRight(1)
@@ -346,11 +349,11 @@ func (p *Pager) onRune(char rune) {
 
 	case 'l':
 		// vim right
-		p.moveRight(16)
+		p.moveRight(p.SideScrollAmount)
 
 	case 'h':
 		// vim left
-		p.moveRight(-16)
+		p.moveRight(-p.SideScrollAmount)
 
 	case '<':
 		p.scrollPosition = newScrollPosition("Pager scroll position")
@@ -492,10 +495,10 @@ func (p *Pager) StartPaging(screen twin.Screen) {
 				p.scrollPosition = p.scrollPosition.NextLine(1)
 
 			case twin.MouseWheelLeft:
-				p.moveRight(-16)
+				p.moveRight(-p.SideScrollAmount)
 
 			case twin.MouseWheelRight:
-				p.moveRight(16)
+				p.moveRight(p.SideScrollAmount)
 			}
 
 		case twin.EventResize:
diff --git a/moar.1 b/moar.1
index 59b6aada..5240d126 100644
--- a/moar.1
+++ b/moar.1
@@ -76,6 +76,9 @@ in caps will be interpreted as one escape character.
 Example value for faint (using ANSI SGR code 2) tilde characters:
 .B ESC[2m~
 .TP
+\fB\-\-shift\fR=int
+Arrow keys side scroll amount. Or try ALT+arrow to scroll one column at a time.
+.TP
 \fB\-\-statusbar\fR={\fBinverse\fR | \fBplain\fR | \fBbold\fR}
 Status bar style
 .TP
diff --git a/moar.go b/moar.go
index fdf9a4e7..c8c4093a 100644
--- a/moar.go
+++ b/moar.go
@@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"strings"
 	"time"
 
@@ -205,6 +206,21 @@ func parseScrollHint(scrollHint string) (twin.Cell, error) {
 	return twin.Cell{}, fmt.Errorf("Expected exactly one (optionally highlighted) character. For example: 'ESC[2m…'")
 }
 
+func parseShiftAmount(shiftAmount string) (uint, error) {
+	value, err := strconv.ParseUint(shiftAmount, 10, 32)
+	if err != nil {
+		return 0, err
+	}
+
+	if value < 1 {
+		return 0, fmt.Errorf("Shift amount must be at least 1, was %d", value)
+	}
+
+	// Let's add an upper bound as well if / when requested
+
+	return uint(value), nil
+}
+
 func main() {
 	// FIXME: If we get a CTRL-C, get terminal back into a useful state before terminating
 
@@ -226,6 +242,7 @@ func main() {
 	printVersion := flagSet.Bool("version", false, "Prints the moar version number")
 	debug := flagSet.Bool("debug", false, "Print debug logs after exiting")
 	trace := flagSet.Bool("trace", false, "Print trace logs after exiting")
+
 	wrap := flagSet.Bool("wrap", false, "Wrap long lines")
 	follow := flagSet.Bool("follow", false, "Follow piped input just like \"tail -f\"")
 	style := flagSetFunc(flagSet,
@@ -246,6 +263,7 @@ func main() {
 	scrollRightHint := flagSetFunc(flagSet, "scroll-right-hint",
 		twin.NewCell('>', twin.StyleDefault.WithAttr(twin.AttrReverse)),
 		"Shown when view can scroll right. One character with optional ANSI highlighting.", parseScrollHint)
+	shift := flagSetFunc(flagSet, "shift", 16, "Horizontal scroll amount >=1, defaults to 16", parseShiftAmount)
 
 	// Combine flags from environment and from command line
 	flags := os.Args[1:]
@@ -363,6 +381,7 @@ func main() {
 	pager.UnprintableStyle = *unprintableStyle
 	pager.ScrollLeftHint = *scrollLeftHint
 	pager.ScrollRightHint = *scrollRightHint
+	pager.SideScrollAmount = int(*shift)
 	startPaging(pager)
 }